To drive an alternating-current motor using a direct-current voltage supplied from a direct-current power supply such as a battery, the following is typically performed: the direct-current voltage is stepped up by a converter serving as a voltage transformer, and then converted to an alternating-current voltage by an inverter before it is applied to the alternating-current motor. Alternating-current motor drive control modes as used in such cases mainly include pulse width modulation (PWM) control and rectangular wave control.
For example, Patent Document 1 discloses driving a motor by switching to the control mode with less loss in an inverter or a motor when it is in a motor operation region in which the motor can be driven either through PWM control or through rectangular wave control.    Patent Document 1: JP 2004-166415 A